One option no one mentions is power to the start contactor directly from the battery.  When I routed 12v. from battery (Odyssy 680) to main relay then to starter contactor, I had very slow cranking (IO360 on Lancair 360).  Battery direct to starter relay and no problem.  Bingelis book shows this option.  Why run starter current through master relay?  How often does a start contactor weld itself closed?  If it does the battery will go flat pretty quick-am I correct?

Ed Gray Dallas